Not Applicable
Not Applicable
Not Applicable
The present invention relates to an axial piston hydraulic device of the bent axis type, and more particularly, to such a device of the type in which the input-output shaft (xe2x80x9cmainxe2x80x9d shaft) defines socket members for receiving the forward ends of piston connecting rods.
As used herein, the term xe2x80x9caxial pistonxe2x80x9d will be understood by those skilled in the art to mean and include a hydraulic device in which pistons reciprocate within a rotatable cylinder barrel, the axes of the pistons being at least generally mutually parallel. Furthermore, references herein and in the appended claims to an axial piston device will be understood to mean and include such devices which are used as both motors and pumps.
An axial piston pump or motor of the xe2x80x9cbent axisxe2x80x9d type is one in which the axis of the input-output shaft is coaxial with the axis of rotation of the cylinder barrel only when the device is in its zero displacement condition. Achieving a positive displacement condition involves pivoting the entire rotating group (i.e., the cylinder barrel, pistons, connecting rods, etc.) so that the axis of rotation of the rotating group defines some acute angle relative to the axis of rotation of the input-output shaft. As is well know to those skilled in the art, the greater the angle of displacement of the rotating group, the larger the output flow per revolution of the input-output shaft (assuming the device is being used as a pump).
In many applications for axial piston pumps and motors, the bent axis type is preferred because the range of stroke angles is much greater in a bent axis device than in an xe2x80x9cin-linexe2x80x9d axial piston device (i.e., one in which the axes of the shaft and the rotating group remain coaxial, and displacement is varied by tilting a tiltable swashplate). By way of example, the typical maximum displacement for commercially available in-line axial piston devices is in the range of about twenty degrees, whereas bent axis piston devices frequently operate at maximum displacements in the range of about forty-five degrees.
As is well known to those skilled in the art, the leakage area of an axial piston device is fairly constant, such that as stroke angle increases, the amount of leakage per unit volume decreases. Therefore, the higher the stroke angle, the greater the overall efficiency of the device. As a result, many of those skilled in the art are constantly seeking design improvements which will permit an increase in the maximum possible stroke angle of bent axis axial piston devices, which also permits a greater range of flows for a given unit size.
In some relatively lower performance bent axis axial piston devices, the balls at the forward ends of the piston connecting rods are merely received within hemispherical openings in the flange of the input-output shaft. However, in relatively higher performance devices, such as where the operating pressure is relatively higher, or the unit is operating at a greater speed, or there is a desire for a greater overall efficiency, each of the connecting rod balls is received within a socket member disposed in the flange of the input-output shaft. As a result, the flange of the input-output shaft can be selected for characteristics such as overall fatigue strength, whereas the socket member can be selected for characteristics which are important in regard to the engagement between the connecting rod ball and the socket member.
Accordingly, it is an object of the present invention to provide an axial piston device of the bent axis type which is able to achieve a greater maximum stroke angle than was possible with the prior art devices.
It is a more specific object of the present invention to provide such an improved axial piston device of the type which utilizes socket members for receiving the ball portions of the piston connecting rods.
The above and other objects of the invention are accomplished by the provision of an axial piston device of the bent axis type comprising a housing, a main shaft rotatably supported relative to the housing, and defining an axis of rotation. A cylinder barrel is rotatably disposed within the housing, the cylinder barrel defining a plurality of mutually parallel cylinders, a piston reciprocably disposed in each cylinder for axial displacement therein, and the cylinder barrel being mounted to be pivotable within the housing relative to the axis of rotation. A universal type connection is operable to transmit rotational movement between the main shaft and the cylinder barrel as the cylinder barrel pivots through its range of motion between a minimum displacement and a maximum displacement relative to the axis of rotation. A plurality of connecting rods is arranged to correspond generally to the cylinders, each connecting rod having a pivotable connection to one of the pistons and including a ball portion pivotably received within a socket member fixed relative to the main shaft.
The improved axial piston device is characterized by each of the socket members defining an axis, each axis being oriented outwardly at an acute angle relative to the axis of rotation of the main shaft, thus permitting an increase in the maximum displacement of the cylinder barrel relative to the axis of rotation.